Chiral alcohols are well known intermediates having good demand as precursors in the development of pharmaceutically important drugs and agrochemicals. Key intermediates can be obtained by resolution of the recemate by chemical as well as by biochemical methods. In procedures which involve resolution of the racemate there is always 50% of the unwanted enantiomer. Hence, it is important to develop methods of asymmetric synthesis which do not allow for the formation of the unwanted enantiomer (50%). Asymmetric reduction of prochiral ketones to give a single enantiomer is one solution to this problem.
Asymmetric reduction of prochiral ketones by chemical methods involve use of expensive chiral reagents. Biocatalytic approach is the most suitable method for preparation of a wide range of chiral alcohols. Baker's yeast is by far the most widely used microorganism for reduction of prochiral ketones to the corresponding optically active alcohols. Here, recovery of desired product from emulsion is cumbersome and at times use of costly co-factors become necessary. These co-factors have to be subsequently regenarated.
Plant cell cultures represent an important potential to perform biochemical reaction on organic compounds. Most of these reactions so for, have been confined to the biotransformation of secondary metabolites produced by plant cell. There have been a few examples of the biotransformation of synthetically important foreign substrates (Tetrahedron Asymmetry 1996, 7, 1571).
Baldassarre et al., have reported the use of whole plant cell for the asymmetric reduction of prochiral ketones (J. Mol. Catal. B: Enzym. 2000, 11, 55–58). Use of immobilized plant cell cultures as potential biocatalyst for the transformation of synthetically important foreign substrate was also investigated (Phytochemistry 1991, 30, 3595, Phytochemistry 1994, 35, 661).
In our attempts to produce chiral alcohols in high enantiomeric excess and high yield, we have investigated several soaked edible grams as potential biocatalysts for the asymmetric reduction of prochiral ketones. We found for the first time that the soaked phaseolus aureus L (green grams) could be effectively used as biocatalyst for the asymmetric reduction of prochiral ketones to obtain chiral alcohols in moderate yields with good enantiomeric selectivity, whereas phaseolus mungo L (black grams) and cicer arietinum L (bengal grams) gave low enantioselectivity with a negligable yield.